Drag type core drill for pavement or rock having disparate inclusions



Jan. 27, 1970 J. L. KELLY. JR

DRAG TYPE CORE DRILL FOR PAVEMENT OR ROCK HAVING DISPARATE INCLUSIONS 7Sheets-Sheet 1 Filed March 20, 1967 550E NW "N AW \N I 5 O A. NM .0 mm.555 m q a m m 2 w: mm M 5 h- E a V L Q VN H @N I 2A h a JOSEPH L.KELLY, JR.

IN VENTOR.

Jan. 27, 1970 J. L. KELLY, JR 3,491,844

' DRAG TYPE CORE DRILb FOR PAVEMENT OR ROCK HAVING DISPARATE INCLUSIONSFiled March 20, 1967 7 Sheets-Sheet 2 Jam FIGURE 2 JQSEPH L. KELLY, JR.

INVENTOR.

ATTORNEY LI -.Y. JR W 3,491,844

FOR PAVEMENT 0R ROCK ATE INCLUSIONS Jam-27,1970 J KE DRAG'TYPE COREDRILL- HAVING DISPAR Filed March 20,. 1967 7 Sheets-Sheet 3 FIGURE 5FIGURE 3 FIGURE 6 FIGURE 4 JOSEPH L. KELLY, JR.

INVENTOR.

B WM ATTORNEY L KELLY. JR 3,491,844

Jan. 27, 1970 J,

- DRAG TYPE CORE DRILL FOR PAVEMENT OR ROCK HAVING DISPARATE INCLUSIONSFiled March 20, 1967 7 Sheets-Sheet 4 FIGURE 11 ;WAVY CUT gSMOOTH CUT YFIGURE 7 WAVY CUT SMOOTH CUT v L x FIGURE 8 JOSEPH L. KELLY, JR.

I N VEN TOR.

ATTORNEY 111.27, 1970 J, ELLY, JR 3,491,844

DRAG TYPE CORE DRILL FOR PAVEMENT OR ROCK HAVING DISPARATE INCLUSIONSFiled March 20, 1967 7 Sheets-Sheet 5 TRAVE L 10 FIGURE 10 FIGURE 9PRIOR ART CONVENTIONAL JOSEPH L. KELLY, JR.

INVENTOR.

y gx,

ATTORNEY Jan. 27 1970 K L JR 3,491,844

DRAG TYPE CORE DRILL FOR PAVEMENT OR ROCK HAVING DISPARATE INCLUSIONSFiled March 20, 1967 7 Sheets-Sheet 6' vv\ 7 W69 x! V 4' r FIGURE 12JOSEPH L. KELLY, JR.

INVENTOR.

ATTORNEY Jam-27,1970 J. L. KELLYFJR DRAG TYPE-CORE DRILL FOR PAVEMENT.ORROCK HAVING DISPARATE INCLUSIONS Filed March 20., 1967 7 Sheets-Sheet 75'-2OT-EVEN s'- IOT- EVEN 5' -1OT-ODD FIGURE 13a FIGURE 13b FIGURE 13cPRIOR ART PRIOR ART 2" 5T'ODD 5"13T'ODD 5" QTQDD FIGURE 13d FIGURE I38FIGURE 13f s 4 5" 7TQDD 5" STQDD FIGURE 13g FIGURE 13h JOSEPH L. KELLY,JR.

INVENTOR.

ATTORNEY United States Patent 3,491,844 DRAG TYPE CORE DRILL FORPAVEMENT OR ROCK HAVING DISPARATE INCLUSIONS Joseph L. Kelly, Jr.,Dallas, Tex., assignor to Hughes Tool Company, Houston, Tex., acorporation of Delaware Filed Mar. 20, 1967, Ser. No. 624,550 Int. Cl.E21b 9/16, 19/08; E21c 1/10 US. Cl. 175-398 9 Claims ABSTRACT OF THEDISCLOSURE The basic drill is a core barrel having the general shape ofa thick-walled cylindrical shell having a multiplicity of cutter bladessecured to the barrel at substantially a common radius and dependingfrom its lower end. The barrel is secured to a square kelly bar whichextends up through a rotary table and has a hydraulic crowd cylindersecured to its upper end. The crowd cylinder is disposed within avertical mast which is tilted down to the bed of a truck for movementbetween drilling sites. The entire drilling rig is slidable on a wiggletable which is pivotably secured to the truck bed.

The invention lies in the structural modifications to reduce oreliminate vibrations, in particular by using a number n of cuttingblades spaced from one another by unequal pitches, defining a pitch asthe angular spacing between any pair of cutter blades, including bothnonadjacent pairs and adjacent pairs. Vibration is reduced as the numberof ditferent pitches S is increased to approach the maximum number ofsuch different pitches, n(n1). The inventor has also discovered thatvibration may be substantially eliminated with a lesser value of S,greater than and preferably greater than The present invention isappropriately classified with surface core drills which are rotatedabout the central axis of the drill but are not equipped with means togrip and retrieve the core.

Another name which could be used is kerf drill, as the cutters of theinvention are mounted on an annular crown or barrel which is rotated todrill an annular kerf until the complete thickness of pavement ispenetrated and the core portion is thus broken loose. Such drills havemany uses, an outstanding one being the forming of access holes inroadbeds for maintenance work on various types of pipelines. A similaremployment is repair work on the pavement itself, the drill being usedto define and separate a core of damaged pavement which is then replacedwith new concrete or similar paving material. It may also be used toharvest minerals, form foundation holes for piling, bore tunnels,ventilation holes, mine raises, and the like.

The present invention resulted from applicants engagement to design anew type of pavement drill, one capable of drilling paved roadways toform openings of the order of 2 to 5 feet in diameter. Prior to theinvention almost all such pavement drilling was done with the well knownjackhammer, an air operated type of percussion drill, and those who mustmake holes in pavement de- 3,491,844 Patented Jan. 27, 1970 manded adrilling machine free from many of the objectionable characteristics ofjackhammers. Since the drill was often to be used in metropolitan areashaving high population densities, a prime requirement was that the drilloperate at a low noise level, much lower than the almost deafeningdecibel level of a jackhammer. It was also to operate quickly, so thatno individual street area would be preempted and no vehicular trafficthereover would be restricted or detoured more than a reasonably shorttime. Flexibility was also demanded, as the roadway area to bepenetrated would sometimes be located adjacent a steep curb or next to abuilding. Mobility was also required, both to get maximum duty from thedrill by moving it quickly from one site to the next and again tominimize the time when any one area is occupied by the drillingequipment, this object in turn to be aided by providing equipmentrequiring minimum times for both installation and removal.

Additional objects were to provide a pavement drill (1) capable ofpenetrating a paved area with a minimum of crack propagation into areasof pavement adjacent and outside the opening being formed, (2) operatingwith a minimum discharge of dust into the atmosphere but withoutreleasing large quantities of drilling fluid onto the pavement, (3)equipped with cutters having an economical service life under even themost difiicult conditions, the cutters to be mounted so that when theybecame worn they could be replaced in a matter of seconds, (4) sodesigned that the drill barrel could be quickly assembled ordisassembled from the rest of the equipment, making it possible toexecute with dispatch a decision to change from one hole size toanother, (5) mounted on a truck of such weight that the total grossweight would permit the rig to travel over and be used on any pavedstreet in a completely legal manner, i.e., without exceeding any maximumweight limit established by competent highway authority. This objectimplied a light weight drilling rig and met with considerable skepticismon the part of the inventors colleagues, who predicted extremely roughoperation and excessive vibration.

Such forecasts were rather fully borne out in an early prototype of apavement drilling machine designed by the present inventor, whosucceeded in eliminating the predicted vibrations only by the use of theinvention to be described. The stated objects were obtained by providinga rotary drilling rig mounted on the bed of a medium size truck,together with its power supply, drive train, tiltable and swingablemast, and all auxiliary equipment such as jacks, hydraulic cylinders,and even a water tank and circulation lines to cool the drill and flushout the cuttings. Quiet operation and compactness were partiallyattained by using continuously cooled drag type cutting blades and amufiled internal combustion engine as the prime mover turning ahydraulic pump and providing hydraulic components to perform allsecondary operations-rotate the drill stem, crowd the drill stem intothe pavement, tilt and swing the mast, operate the jacks, etc. The mastlies flat on the truck in transport position, with the core barrelslightly overhanging the rear end of the truck, and is moved further tothe rear and then tilted to a vertical position just behind the rear endof the truck when a drilling operation is to be started. Inaccessibleareas of pavement are reached by swinging the mast approximately 10degrees to either side of the center line of the vehicle. The timerequired for either set-up or breakdown is only about 5 minutes, thusinsuring low down time on any one drilling site, and the truck mountingmakes for a maximum of mobility.

The rotary equipment provided on this initial assembly will turn thedrill stem at to 20 revolutions per minute (r.p.m.), a rangesufliciently low so that high pitched noises are avoided and yetsufficiently high so that an average drilling rate of about one inch perminute may be maintained in drilling homogeneous concrete with the corebarrel loaded to 18,000 pounds of force. With the usual quantity ofspaced apart inclusions, an 18- inch pavement can be cored through in 30minutes or less. The core barrel itself is simply a thick-walledcylindrical shell having its lower end notched at variouscircumferential locations to define pockets for the mounting ofreplaceable drag blades which extend below the barrel and somewhatoverhang both its inner and outer surfaces.

The need for certain features of the present invention became apparentwhen the aforementioned prototype of the drilling equipment thus fardescribed was given its initial field tests. In such tests the drilloperated with a great deal of vibration, most of it in the verticaldirection. This was not only noisy, but the vibrations were transmittedupwardly through the drill to cause tremendous shaking of the equipmentmounted on the truck bed. Threaded connections became loose, someconnecting members failed in shear, and in general the high amplitudevibrations threatened to tear up the whole assembly.

The concrete for such tests had the usual steel reinforcing (rebars)embedded in it, and it quickly became apparent that the unwelcomevibrations had some causal relationship with such rebars and theirinteraction with the cutting blades. Just what this relationship was,however, was not immediately apparent, nor was it at all obvious thatsomething could be done to eliminate the vibrations and save theequipment from destroying itself.

A general concept built into embodiments of the pres ent invention toreduce such vibrations is that of increased structural rigidity. Twomeans contributing to such greater rigidity are known in the prior artbut are described here because they are the exception rather than therule in prior art drilling equipment. One of these means is disposingthe four jacks which support the truck bed and drilling rigapproximately under the corners of this bed. This disposition amounts toa maximum longitudinal spacing of the two sets of jacks (or the fore setand the aft set), and contrasts with the usual arrangement where thefore set, that nearer the cab, is located just forward of the rear truckor bogie. The effect of the usual jack disposition was a tendency of theentire rig to swing somewhat during operation, causing the drill barrelto rub against and bind with the sidewalls of the hole. Changing thejacks to the described maximum longitudinal spacing eliminated orsharply reduced such effect.

The other in this pair of features known in the prior art is thesubstitution of a wiggle table for a turntable as a swingable mount forthe drill, to enable it to be moved to either side of the truck bed forcutting in relatively inaccessible areas. In the mounting of this wiggletable the fulcrum was moved forwardly to a point just short of itsforward end (just behind the truck cab), as contrasted to the usualpivot location in the center of the ordinary table used in mounting suchdrilling equipment as augers. Substitution of the Wiggle table alsocaused a Weight decrease which brought the gross weight on the rearwheels within the legal limit.

One contribution of the present inventor to greater structural rigidity,now to be claimed in a divisional application, involves the connectionbetween the drill barrel and the kelly bar, the central shaft throughwhich torque and thrust are transmitted to the core barrel. The drillbarrel itself is made quite rigid and true, preferably by casting it andmaking it in a relatively thick section, e.g., with a wall thickness ofinch for a 5-foot diameter barrel. In the preferred embodiment to bedescribed, the lower end of the barrel, where the cutting blades aremounted, is made even thicker, e.g., 1- /2 inches, over the lowermostsix inches of length. The kelly bar itself is made square incross-section so that it can gradually slide through the rotary tablewhile being turned by the table through a sliding fit into a squarecentral hole therein. In the preferred embodiment it is made as a hollowmember, e.g., seven inches square with a inch wall, largely to serve asa conduit through which water is circulated down to the barrel and thedrag blades. Although it has been postulated that the connection'betweenthe drill barrel and the kelly bar can be a relatively loose slip fit,in embodiments of the present invention it was found that the oppositeapproach of increasing the rigidity of the connection by making it aforce or press fit reduced vibration and caused the drill barrel to cuta truer kerf.

Another novel aspect conceived by the present inventor, now to beclaimed on the aforementioned divisional application, deals with theproblem of making control adjustments when the drill encounters changedconditions. This contribution deals in particular with drilling througha section of homogeneous concrete and into a section containingreinforcing bars or other disparate inclusions. The word disparate isused because the only characteristic of such things as steel rebars andlarge pieces of hard aggregate which make them more difficult to drillis the fact that they are different from the bulk of the material inwhich they are embedded. They are not particularly harder or tougher todrill than concrete, and a block consisting entirely of steel orlimestone presents no very great problem to a driller. The problem seemsto lie solely in the fact that they are spaced apart in a fundamentallydifferent matrix.

The usual prior art technique was to deal with the changed situation byvarying the thrust load in response to a harder drilling condition,specifically by ,drilling off and then bumping (respectively themanipulation of the controls to lift the drill until the cutters arebarely free of contact with the bottom of the annulus, andintermittently lowering the drill so that it contacts and cuts bottom inshort spaced apart bursts of power application, being lifted off bottombetween cutting bursts). In using this technique the operator acceptswhatever penetration rate results, while by contrast in the presentinvention the opposite technique is employed, namely the penetrationrate is controlled and the thrust magnitude is allowed to vary asrequired to maintain a penetration rate dictated to the controls by theoperator. When more .difiicult drilling is encountered, the controls areset so that a lower penetration rate obtains. This approach was ,asignificant departure from standard drilling practice,

but resulted in successful drilling while the prior art practice causedrough drilling and frequent stalls.

The significant contribution claimed herein lies in another structuraldeparture from the prior art aimed at reducing or eliminating roughrunning and excess vibration. This contribution lies in the spacing ofthe cutter blades about the circumference of the core barrel, a spac:ing aimed at minimizing or reducing the amplitude of the longitudinalmovement of the barrel as it passes over inclusions such as reinforcingbars. In prior art drills such spacing is for the most part uniform,i.e., the angular distance or pitch between one pair of adjacent bladesis equal to that between all other adjacent pairs. Embodiments of thepresent invention, on the other hand, utilize at least some unequalpitches and preferably all of the pitches so dimensioned that there isrelatively little duplication. The ultimate in such unequal spacing isto select all of the pitches so that each pitch is unequal to all of theothers and each possible sum of consecutive pitches up to one less thanthe total number of teeth is unequal to both each individual pitch andeach other such sum of pitches. Total compliance with this criterion isnot absolutely essential, but the more closely it is ap .5 proached themore certainly smooth running will be assured.

Another way of stating the invention is by thinking of a blade pitch asthe angular spacing between any pair of blades, whether the members ofthe pair are adjacent or non-adjacent. Using this definition andmeasuring blade No. 1 of a S-bladed drill, it will be apparent thatthere are 4 pitches-No. 1 to No. 2, No. 1 to No. 3, No. 1 to No. 4 andNo. 1 to No. 5. Similarly, there are 4 pitches when blade No. 2 is usedas a reference, 4 for No. 3, 4 for No. 4 and 4 when blade N0. is thestarting point. In short the total number of pitches is 5 4=20, orn(n-1). Each of these 20 pitches can be chosen to be diflerent from theother 19, and the present inventor has found that vibration iseliminated as S, the number of unduplicated pitches, approaches n(nl).He has also found that smooth running is substantially insured when S isgreater than and preferably greater than A subsidiary (and claimed)feature is the mounting of the cutter blades for ready replacement. Toaccomplish such replaceability the massive base of the cutter is formedwith at least one laterally protruding lug or flange designed to engagea corresponding shoulder of the core barrel to prevent axial movement ofthe blade. With a single such flange the base of the blade has thegeneral shape of an -L. In one preferred embodiment, the cutter bladebase is formed with a pair of oppositely extending flanges, giving itthe shape of a T, and a similarly shaped slot is formed in the loweredge of the drill barrel, the T being formed so that an observer sees aT outline when looking inwardly along a radius of the barrelwith thecross bar above the central vertical leg. To hold the cutter in placeagainst radial movement a pair of registering vertical holes are formedin blade and barrel, and a pin of appropriate size is disposed to extendthrough such aligned holes. The hole in the barrel is elongatedvertically so that the whole of the pin may be pushed up into the holeduring a changeover of blades, and it is preferably biased to a normallyprotruding position by a spring also disposed in the elongated opening.In a second embodiment the pin and spring are replaced by a machinescrew extending through a hole in the blade and engaging a threaded holein the barrel, vibrational loosening being prevented by a locking memberin the threads, e.g., a plastic plug disposed in a transverse hole andextending into the threads. This embodiment has the advantage of lowercost resulting from the elimination of machining operations, the entiremanufacture of the blades being by forging plus the brazing of thecarbide cutting inserts.

These and certain other features of the invention will perhaps becomemore readily understood by a scanning of the attached drawing, in which:

FIGURE 1 is a left side perspective elevation of the entire drillingmachine in a drilling attitude, complete with its truck support,

FIGURE 2 is a bottom end view of the core barrel,

' looking up into the barrel from its cutting end, only one cutter bladebeing shown in a slot,

FIGURE 3 is a sectional elevation of a preferred cutter blade assemblyas disposed in the drill barrel, the sectioning plane passing through acircumference midway between the inner and outer surfaces of the barrel,as indicated by the lines and arrows 33 of FIGURE 2.

FIGURE 4 is a perspective view of the cutter blade of FIGURES 2 and 3,

FIGURES 5 and 6 are similar views of a second cutter assembly and blade,respectively, a vertical section and a perspective view, this cutterbeing secured to the core 6 barrel against lateral movement with anordinary machine screw,

FIGURE 7 is a fragmentary plan view showing both a true cylindrical kerfcut by the apparatus of the present invention and a wavy kerf cut bydrilling apparatus lacking the improvements of the invention,

FIGURE 8 is a fragmentary elevational section, somewhat schematic inform, showing both a smooth bottom as achieved with the presentinvention and a wavy or sinusoidal bottom which is likely to result fromthe use of prior art devices or methods,

FIGURES 9 and 10 are schematic plan views of drilling apparatus mountedon a wiggle table which in turn is mounted on a truck bed, respectivelyshowing the conventional and unconventional locations of the pivotalmember.

FIGURE 11 is an elevation, partly in section, showing the connectionbetween the drill barrel and kelly bar,

FIGURE 12 is a schematic diagram of the hydraulic circuit for the crowdcylinder, and

FIGURE 13 is a group of schematic views of the cutter blade locations,some of which illustrate cutter spacings which resulted in rough runningwhile other views show cutter spacings according to the concepts of thepresent invention which resulted in smooth operation, virtually withoutvibration.

Turning now to the drawing for a more detailed description of theinvention, FIGURE 1 is a side view of the complete truck mounteddrilling rig. The major components of the complete machine are cab 1,trailer or truck bed 2, the wiggle table 3 which supports all of thedrilling equipment, the gasoline engine prime mover 4, the hydraulicfluid reservoir 6 which supplies fluid to the pump (not shown), thedrilling mast 7 which contains the vertically disposed crowd cylinder(not visible) in its upper portion and the top part of the square kellybar in its lower portion, the rotary table 8 through the center of whichthe kelly bar extends, kelly bar 9, and core barrel 11. Also shown inFIGURE 1 are water tank 16, control console 17, auxiliary hydraulicwinch 18 for service line 19, forward jacks 21 and aft jacks 22, and awater pump 23 and swivel 24 for connecting water line 26 to kelly bar 9.Not visible are the main hydraulic motor which is coupled to the rotarytable by appropriate gearing and the main hydraulic pump driven byengine 4. The water tank 16 supplies water to the core barrel forcuttings removal and dust suppression through pump 23, line 26, swivel24 and kelly bar 9.

The wiggle table 3 (see FIGURES 1, 9 and 10) is essentially a pair ofparallel rails 31, appropriately cross braced and pivotably supported ona fixed framework on the truck bed. As previously indicated, thevertical pivot point 36 is located just behind cab 1, giving the drillat the opposite end of the pair of rails the maximum linear travel forany given angle of rotation. The rails 31 act as ways for the drillingrig, allowing it to be slid rearwardly preparatory to raising the mastand forwardly preparatory to moving to another location. Ordinarily theyare disposed parallel to the longitudinal axis of the truck, but a pairof hydraulic cylinders 32 are provided to permit their rotation in ahorizontal plane through an agle of about 10 degrees from either side ofcenter. Each such cylinder is normally disposed in a slanted positionrelative to the truck longitudinal axis with one end of the cylinderpivotably secured to the fixed framework on the truck bed at 33 and thepsiton rod 34 extending from such cylinder pivotably fixed to theadjacent rail 31. The two cylinders 32 and piston rods 34 are thusdisposed to point rearwardly and inwardly so that their extended centerlines would converge and meet approximately on the longitudinal centerline of the trailer. To swing the table 3 (i.e., rails 31) to one sideof center, one of the piston rods is extended further than normal fromits associated cylinder while the other piston rod is at the same timeretracted into its cylinder. In a swing to the opposite side of center,of course, the directions of extension or retraction of the two pistonrods are reversed.

The difference between the wiggle. table mounting used with embodimentsof the present invention and of the prior art will be apparent from acomparison of FIG- URES 9 and 10, which respectively show a wiggle table3 as pivotably mounted at 36 according to conventional practice and thewiggle table 3 mounted at 36 in drilling machines actually built andtested. In the two figures the core barrel 11 or 11 has been moved thesame distance laterally from its normal position shown in dashedoutline, but to accomplish this the usual prior art table 3 must berotated through a larger angle than the wiggle table 3 used with theinvention. In addition, the disposition of the employed structure ismore stable because a greater reaction load up through the barrel isrequired to rock the rig in a vertical plane. To reduce the liklihood ofsuch rocking the rear end of the wiggle table is provided with anoverhanging lip (not shown) which projects beneath an adjacent member ofthe fixed framework of the truck bed.

A connection between core barrel 11 and kelly bar 9 is illustrated inFIGURE 11. Top plate 41 of the barrel terminates inwardly in adownwardly extending short cylindrical sleeve 40 which is tightlycoupled to a similarly shaped adaptor 42 by a ring or circle of spacedapart machine screws 43 extending through the radial annular flange 44of the adaptor and top plate 41. The recess 46 of adaptor 42 is squarein cross section to receive the square kelly bar 9.

In the prototype model the fit of the kelly bar 9 into opening 46 wasrelatively tight, by comparison with the prior art, as a clearance X ofabout & inch was provided. The connection was completed by a tightlyfitting pin 47 extending horizontally through registering openings inthe kelly bar and adaptor. The result was unsatisfactory, causing arotation of the core barrel about pin 47 when hard inclusions wereencountered. The kerf resulting from this condition is the wavy cutshown in the fragmentary plan of FIGURE 7. The present inventioneliminated this undesirable condition and produced the smooth out shownin the same figure by reducing the clearance X to zero, that is bymaking a press fit or force fit between the kelly bar and the corebarrel.

With respect to the feature of the invention involving controlling thepenetration rate of the drill rather than the magnitude of the thrust,it should be noted that many diflerent means can be used to accomplishsuch control. An applicable hydraulic circuit is shown in FIGURE 12, butit should be understood that such circuit is only illustrative. In thecircuit of this drawing figure hydraulic fluid is supplied by pump 6through valve 61 to the upper end of crowd cylinder 62, and such fluidacts on piston 63 to exert downward thrust through piston rod 64 andkelly bar 9 on core barrel 11. The volume of fluid thus supplieddetermines the thrust rate (penetration rate), and is controlled by flowcontrol or bypass valve 66. Fluid leaving the lower end of crowdcylinder 62 passes through relief valve 67 and main valve 61 to returnto the Pump through tank 16.

Relief valve 67 is set so that it will stay closed when the pressure incrowd cylinder 62 below the piston is less than that caused by theweight of the system pendent from the piston, i.e., the barrel 11, kellybar 9, piston rod 64 and piston 62, and will open to permit flow out ofthe lower end at some preset higher pressure. This insures positivecontrol when the required thrust is less than such suspended Weight,i.e., the penetration rate is totally dependent on the rate at whichhydraulic fluid is supplied to the upper end of the cylinder. Forexample, suppose the weight of the suspended system were 3200 pounds andthe cross-sectional area below the piston were 16 square inches,indicating that a pressure of 200 p.s.i. is needed below the piston tosupport the suspended system. If valve 67 were to be set to permit flowout of the bottom of crowd cylinder 62 at some reduced pressure lessthan 200 p.s.i., core barrel 11 would always have to sit on bottomduring a drilling operation. This would prevent the operator from usingthe drill as a milling machine, a mode of operation necessary for such acondition as a brokenoif rebar which has snapped back so that aconsiderable length of it at the broken end lies in the kerf. If thecore barrel must remain on bottom, as it rotates a cutting blade overthe concrete the blade plows into the frayed end of the rebar, verylikely either breaking the blade, stalling the machine, or both. In theactual mode of operation employed, the cutting blades are held slightlyolf bottom so that they contact only the frayed rebar, and they drill orgrind through it at a set rate of penetration.

Gage 68 is a pressure gage which enables the operator to read the thrustload and thus maintain a rate setting which the drill can maintain. Ifthe drill were unable to maintain the rate demanded by such a setting,the piston 63 would nevertheless continue to move downwardly relative tocylinder 62, but the thrust would increase to cause crowd cylinder 62,mast 7, and the entire rig to be raised up and supported by the corebarrel and kelly bar, a highly undesirable condition because when thisOccurs the operator loses control of both the rate of advance and theposition of the machine. In practice the operator avoids such a resultby adjusting valve 66 to bypass a larger fraction of fluid therethrough,thus reducing both the pressure at the top of cylinder 62 and the flowof fluid therethrough. The check valve 69 is provided to bypass valve 67and permit the reverse flow of fluid through cylinder 62 to retractpiston 63 and thus the kelly bar and core barrel. Valve 70 is a reliefvalve which protects pump 6, and is similar to valve 67 in operation. Itwill be apparent to one of average skill in the art that the setting ofrelief valve 70 can be such that the maximum pressure delivered to crowdcylinder 62 will be less than that required to lift the rig off theground and thus prevent the undesirable condition mentioned above.

If the described circuit were to be modified to a system where thrustrather than thrust rate is controlled, valve 66 would be replaced by apressure responsive valve having the effect of maintaining a particularpressure in the hydraulic line leading to the upper part of crowdcylinder 62 for a particular setting of the valve (rather than causing aparticular flow rate in this line, according to the invention). Such asystem is undesirable in drills of the present invention, characterizedas they are by light weight and thus by a small number of cuttingblades, because it produces frequent stalls. Since the material beingcut is non-homogeneous, the thrust required at one elevation is greaterthan at another. When rebars are encountered the concrete between themis cut quickly but not the rebars themselves. The drill rides up anddown over each rebar, causing longitudinal vibrations and frequentstalls. As an example of the control system of the invention, the valvesof the described system were set to give a penetration rate of /1 to 1inch per minute in cutting through pavement having no rebars or otherhard inclusions, using the 5-foot diameter core barrel and turning it at12 to 14 revolutions per minute. For this part of the cutting the flowrate into and out of the crowd cylinder was about .085 gallon per minute(g.p.m.) and the pressure gage 68 read 1200 p.s.i. When the drill thenencountered a rebar, as evidenced first by a screeching noise and than aregular thumping, the operator reduced the flow rate to .031 g.p.m. toobtain a penetration rate of about inch per minute and a pressurereading of 400-500 p.s.i. between intervals of contact with the rebar.With such reduced penetration rate, the rebar was cut through withoutappreciable vibration or other undesirable incident.

The cutting blades 71 mounted in the lower edge of core barrel 9 areshown in detail in FIGURE 4, and the manner in which they are mounted inthe barrel is shown 9 in FIGURE 3. The blade itself is a massive bit ofsteel presenting a vertical leading surface 72 disposed approximately ina radial plane of the axis of the drill (actually with a degree negativerake). The cutting tip of the blade is chisel shaped with apex 73displaced only slightly from the center of the blade. While blades madeentirely of steel may be used, the preferred and illustratedconstruction utilizes an insert 74 of such wear resistant material ascast or sintered tungsten carbide to define the cutting structure. Thelower edges 76 of the insert are preferably formed with a small draftsloping away from leading surface 72, also as illustrated.

The base 77 of blade 71 is provided with the short tongues 78 extendingoutwardly below the leading face 72 and the trailing face opposite face72, thus giving base 77 the general shape of a T. Slots 81 in the loweredge of core barrel 9 are formed with a similar shape, the clearancesbeing such that blades 71 are generally inserted into slots 81 with asnug fit. Any movement parallel to the vertical axis is therebyprevented, and similarly the blade can not move in a circumferentialdirection, but to prevent radial movement of the cutters somethingadditional must be provided. The securing means of the invention is alocking pin 82 disposed in the registering vertical holes 79 in theblade and 83 in the barrel. Movement of the pin during operation of thedrill is prevented by the shoulder engagement of its oversize diameterportion 84 with the surface surrounding the upper end of hole 83,together with the action of spring 86 in urging the pin downwardly. Theupper part 8-7 of opening 83 is made oversize to accommodate spring 86as it surrounds the pin and seats at one end against the upper end ofopening 87 and at the other end against the upper surface of theenlarged knot 84 on pin 82. In mounting or disassembling blade 71,locking pin or plunger 82 is pushed upwardly into openings 83 and 87against the increasing compressive force of spring 87 until it clearsopening 79 in the blade, whereupon the blade may be pushed radiallyinwardly or outwardly. Sleeve 88 is made as a separate piece simplybecause of the necessities of assembly, and is force fitted into thecounterbored lower end 89 of the opening as a permanent assembly.

With respect to the tooth (blade) spacing improvement of the invention,it may be mentioned that in early prototypes having uniform spacings thecore barrel bounced vertically with a frequency per revolutionapproximately equal to the number of blades used. The result was a wavyor sinusoidal bottom, as so drawn and labeled in FIG- URE 8. It appearedthat this type of bottom pattern was resulting from the drillsencountering and attempting to drill through disparate inclusions suchas rebars. When the first tooth out of, e.g., 20, struck the rebar itwould ride up over the inclusion, raising the entire barrel and rig andfalling ofi the distant side of the rebar with a sharp blow that wouldcause all of the blades to make similar dents in the concrete at theirindividual spacings from the first tooth. During the rotation of the bitto bring tooth #2 up to the rebar a certain amount of concrete would becut, but as tooth #2 engaged the rebar it too would ride up over toraise the entire rig and cause it and all blades to fall into contactwith the pavement with a sharp blow as tooth #2 slipped off the far sideof the rebar and into the dent or impression started by tooth #1. Atthat particular time, since the pitches for all teeth were equal, tooth#3 would fall into and deepen the impression started by tooth #2 whentooth #1 slid off the rebar, tooth #4 would fall into and deepen theimpression started by #3, and so forth all the way around thecircumference of the core barrel for a total of only 20 impressions. Asthe barrel was further rotated each blade would be raised from thetrough of an ever deepening impression to pass through a crest until thenext trough was encountered, and the result was the build-up of a bottomhole pattern with a continuous succession of troughs spaced apart bycrests. As previously indicated,

10 running the drill over this type pattern resulted in a great deal ofnoise and such a large amount of vibration as to threaten to tear themachine apart.

There are several possible solutions to this vibration problem, but noneof the alternate solutions appear attractive. One is to set the maximumpenetration rate so that the thrust load available will permit uniformcutting of the hardest material anticipated, e.g., the rebars, but thiswould result in an unacceptably low average penetration rate. The sameresult would obtain if the unit load per tooth weredecreased byincreasing the number of teeth (more or less like converting the drillto a saw). The opposite approach of decreasing the number of teeth wouldbe feasible for small drills, but would not work for core barrels aslarge as 5 feet in diameter because the cutter spacing could be so highthat it would be too difficult to start cutting the kerf unless a guidecollar were available. It is also not feasible to rely entirely ondecreasing the penetration rate when hard material is encounteredbecause of the high frequency of encounters between rebars and cuttingblades.

The actual solution to the problem, and the major contribution of thepresent invention, was to so unevenly space the cutters that smoothrunning was obtained and excessive vibration was eliminated. The conceptis to so space the cutters so as to minimize (or approach a minimumuntil smooth running obtains), during a complete revolution of the corebarrel, the number of times the various teeth fall into impressions madeby other teeth.

Another way of stating it is to say that the desired end is to maximizethe number of separate impressions made by the teeth during a singlerevolution. Thus if there are 20 teeth the total number of falls of allteeth during one revolution over a single rebar is 20x20 or 400, but toarrive at the maximum possible number of separate impressions this totalmust be reduced by 19 or (20l) because nothing can prevent all 20 teethfrom bouncing into a common impression as they slide over the rebar.Thus for 20 teeth the aim is to make 381 impressions per revolution, andfor n teeth the maximum or ideal number of impressions is n (n- 1).

To compare the ideal number of impressions with the actual numberresulting from an actual spacing, the ratio of the average number offalls per impression is utilized. This ratio is obtained simply bydividing n the total number of falls of all teeth in a revolution, bythe actual number of impressions per revolution resulting from an actualspacing of the n teeth. The closer this ratio approaches unity, the morenearly is the ideal approached. It should be noted that such ratio isindependent of the number of teeth, and thus affords ready comparisonbetween various designs.

The number of falls per revolution caused by any single hard spot willbe minimized if all the pitches between successive teeth and allpossible sums of consecutive pitches up to and including one less thanthe number of teeth are unequal. For example, the number of blows perrevolution will be minimized for a 3-tooth drill having pitches P P andP if the following inequality holds:

For four teeth the inequality required would be:

In general, satisfaction of this requirement will produce n (n-l)separate impressions for n teeth and no impression is subjected to morethan one fall per revolution except the one immediately adjacent to thehard spot.

In practice, absolute compliance with this spacing has not provednecessary. The following table summarizes the tooth arrangementsactually tested and the running conditions that resulted from each.

TABLE I No. of impressions Avg. N 0. falls per rev. per Barrel No. ofConsecutive impression Runnlng Line dia., it. teeth pitches, degrees*Ideal Actual per rev. condition a 5 20 18 (evenly spaced). 381 20 20Rough. b 5 10 36 (evenly spaced)...- 91 10 10 Do. 72, 18, 18, 54, 18,36, 91 5 Do.

72, 18, 36. d 2 5 75, 75, 75, 75, 60 21 9 2. 78 Smooth. e 5 13 13, 17,20, 22, 24, 26, 157 124 1.36 Do.

36, 38, 40. g 5 7 30, 42, 50, 5s, 66, 74, 40- 43 42 1.17 Do. h 5 5 50,72, 90, 70, 78 21 21 1. 19 Smooth except when starting.

Refer to Figure 13.

The cutting blade dispositions corresponding to those set forth in theabove table are also illustrated in FIGURES 130: through 13h, theletters of the figures corresponding to the lines of the table. It willbe apparent from the observed running conditions that smooth runningresults when the average number of falls per impression is somethingless than five, and preferably is less than three.

The invention can also be explained, without using functionalexpressions, by introducing the symbols P, S and I, where:

Pzthe angular or circumferential dimension between any pair of blades ofcutters, whether adjacent or non-adjacent, excluding, of course, anypitch encompassing 360 or more;

S=the total number of different pitches between all the various pairs ofblades of a complete drill; and

I=the total number of impressions made by all blades in one completerevolution, assuming all of them to fall with the drill as each bladerides over or passes a common index point (and each blade falling intothe same impression at such index point).

It can be shown that I'=S+ 1, simply because an impression made by theblade used as a reference cannot be counted as a pitch.

Using the above criterion that the number of falls per impression in asingle revolution should be something less than five, and preferablyless than three,

Stated in words, the number of different circumferential pitches orspacings between the various combinations of pairs of blades,non-adjacent as well as adjacent, is greater than /5 the square of thenumber of blades less unity. For the less-than-three criterion, thenumber of different such pitches is greater than /3 the square of thenumber of blades, less unity.

To demonstrate the application of this principle, imagine the core drillprojected as a clock, with each blade successively movingcounterclockwise and momentarily stopping at a reference point normallyused for the hour of 12:00. Designate the blade at the reference pointfor the first stop as #1 and, proceeding clockwise, designate the nextblade #2, etc. Then draw up a table similar to the following for theS-blade bit shown in line d of the above Table I, one line for eachmomentary position.

TABLE II Impressions made by teeth at degrees measured clockwise fromreference point It can be seen from this table that when the drill isrotated so that blade #2 replaces blade #1 in the index position, theentire core drill must be rotated 75 and each new position (impression)of any blade is determined by subtracting 75 from the angular positionof that blade in the previous line.

From the Table II it can be seen that the impressions are made at 0 or360 (5 falls), 6 (1 fall), 75 (4), (2), (3), 210 (3), 225 (2), 285 4)and 300 (1 fall). This yields 1:9 impressions Fa1ls=25=5 :n

8:8 because there are different pitches P of 75 (between blades 1-2,2-3, 3-4, and 4-5), 60 (between blades 5-1), 150 (blades 13, 2-4, and3-5), 225 (blades 1-4 and 2-5), 300 (blades 1-5), 135 (blades 4-1 and5-2), 210 (blades 4-2, 5-3, and 2-5) and 285 (blades 2-1, 3-2, 4-3 and5-4).

Thus 9=8+1 or I=S+1z9 (for the 12:00 oclock impression), and

Average Falls n A table similar to Table II for the S-bladed bitdescribed in line h of Table I would show separate impressions at 0, 50,70, 72, 78, 90, 122, 128, 148, 162, 198, 200, 212, 232, 238, 270, 282,288, 290, and 310, or 1:21. By adding up the various pitches betweenadjacent blades it can be shown that 8:20. In this case each impressionexcept that at the reference point experiences only one fall of a bladeduring a revolution. Since each blade must necessarily fall toward theimpression at the reference point, it can be readily seen that themaximum number of separate impressions is equal to n (n-l). In theexample of line h such maximum is obtained, and is equal to 5 (S-1): 21.For this situation the minimum average falls per impression is alsoobtained, being equal to 25/21 or 1.19. For any given number of blades nsuch minimum average blows per impression is for a 3-blade bit beingand, for a 4-blade bit,

gular distance of each blade slot 81 from a common reference slot somarked at the top center of the circumference. It will be noted thateach of the latter set of angles expressed in degrees is a prime number,another criterion which has been found to promote smooth running.

The cutting blade 71' of FIGURE 6 differs from that of FIGURE 4primarily in having only a forwardly projecting base tongue 78, thusgiving base 77' and L-shape in circumferential cross-section. Inaddition, vertical opening 79 has been modified to more of asemi-circular cross section and moved to the rear of base 77' so that itintersects the rear surface, making it more of a groove than a hole. Asshown in FIGURE 5, blade 71' is then secured against radial movement bya cap screw 80 disposed in opening 79 and extending into and threadedlyengaging hole 85 in barrel 11.

It can also be mentioned that a very satisfactory blade cooling and dustlaying system was provided by the water tank mentioned earlier and awater line running to the inside of the barrel. A circulation rate ofless than 2 gallons per minute quite satisfactorily cooled the bladesand flushed out the cuttings. This low rate caused no water overflow tosurrounding paved areas, nor did it cause a pool of water to accumulateand run into the hole after the coupon (core) was cut. The waterrequired simply mixed with the cuttings to form a thin paste which waseasily disposed of by the drilling crew. Attempts to supply the waterfrom outside the barrel did not cause adequate cooling and cleaning. Ascompared with dry operation, drilling with the water caused :a tenfoldincrease in cutting blade life.

What is claimed is:

1. A core drill for reinforced pavement comprising a thick walledcylindrical core barrel and a multiplicity n of cutter blades secured tothe core barrel to depend from the lower end thereof at substantiallyequal radii from the longitudinal axis of the barrel, said blades beingspaced apart circumferentially so that the total number of differentpitches S between pairs of said blades in a common circumferentialdirection, including pitches be-' tween both adjacent and non-adjacentpairs of blades, is greater than 3. The core drill of claim 1 in whichthere are at least 3 cutting blades.

4. The core drill of claim 1 in which the number of blades 11 is '5 ormore.

5. A core drill for reinforced pavement comprising a core barrel havingthe general shape of a thick walled cylindrical shell and a multiplicityn of cutting blades secured in the bottom =nf said core barrel at acommon radial distance from the center of said drill, said blades beingspaced about the circumference of the core barrel so that there are Sdifferent circumferential spacings between the various pairs of cutterblades, non-adjacent pairs as well as adjacent pairs, the number of theblades n and their spacings S being selected so that n /S +1 is lessthan 5, there being at least one instance where successive pitchesbetween adjacent blades are unequal.

6. The core drill of claim 5 in which said blades are spaced so that thenumber of blades n and the number of different pitches S between thevarious pairs of blades are chosen so that n /S-H lies between 1 and 3.

7. The core drill of claim 5 having n blades spaced apart with Sdifferent circumferential spacings substantially equal to n(n-1).

8. The core drill of claim 5 in which substantially all of the pitchesbetween adjacent blades are unequal.

9. A core drill for reinforced pavement comprising a cylindrical shellcore barrel and a multiplicity of cutting blades secured in the bottomend of said barrel at substantially the same radius with respect to thelongitudinal axis of said core barrel, said cutting blades being spacedabout the circumference of the barrel so that a substantial number oftheir angular distances from a common reference blade, measured indegrees, are prime members.

References Cited UNITED STATES PATENTS 1,663,025 3/1928 Phipps -403890,012 6/1908 Anderson 175-398 1,041,568 10/1912 Bade 175-397 X1,114,497 10/1914 MacDonald 175-413 1,271,396 7/1918 Walker 175-410 X2,649,284 8/1953 Letts 175-410 X 2,756,025 7/1956 Lay 175-413 X2,856,157 10/1958 Chapin et al. 175-410 X 2,918,260 12/1959 Tilden175-403 X 3,118,511 1/1964 Kay 175-397 CHARLES E. OCONNELL, PrimaryExaminer I. A. CALVERT, Assistant Examiner US. Cl. X.R.

